I've been looking around for an Xbox (original) emulator to do some runs of some old racing games, but I haven't found anything that's reliable. Anyone have any suggestions?

That depends on the rules of the game you're running. From what I know, there currently isn't a 100% accurate emulator for the OG Xbox so most games don't allow emulator runs.

There's only two emulator that are even potentially gonna be able to run the game at all, CXBX-R ( https://cxbx-reloaded.co.uk/ ) and XEMU ( https://xemu.app/ ), but there's a fair chance it will not run properly to begin with and it's even less likely whoever moderates said game is gonna accept runs done on such emulators.

Thanks, I'll take a look at those and also ask about using emulators for runs.